Add RADEV2 test results for freedv-gui.

[tmiw]

Performed formal RADEV2 tests using freedv-gui. This PR adds the required documentation for supported platforms/OSes.

[tmiw]

@drowe67 / @peterbmarks: I only added Windows tests for now because I ran out of time. Once I get the signoff for Windows, I'll test on Linux and macOS and update this PR accordingly.

Note: the loopback tests were done automatically by GitHub as part of CI (see https://github.com/drowe67/freedv-gui/blob/ms-rade-v2/test/RadeVerificationReport.ps1 and https://github.com/drowe67/freedv-gui/blob/ms-rade-v2/test/rade_verification_report.sh). The mentioned scripts were also designed with Claude's assistance.

[peterbmarks]

Thanks @tmiw I notice you've patched the USB audio dongle's headphone out directly in to the microphone input. Perhaps my dongles are different but I would have thought this would clip due to the high level in to the microphone?

[tmiw]

Thanks @tmiw I notice you've patched the USB audio dongle's headphone out directly in to the microphone input. Perhaps my dongles are different but I would have thought this would clip due to the high level in to the microphone?

Yeah I mentioned in the report that I had to set speaker and mic levels for that device to 50% in Windows before the test. When they were at 100% (the default), I was getting in the range of 0.130 for loss instead.